The present invention relates to a process for producing a sintered aluminum nitride furnished with via holes. More particularly, the present invention relates to a process for producing a crackless sintered aluminum nitride furnished with highly isolated via holes, having been satisfactorily densified.
The sintered aluminum nitride has excellent properties such as a high thermal conductivity, a favorable electrical insulation and a thermal expansion coefficient substantially equal to that of silicon (Si) for forming integrated circuits. Therefore, the sintered aluminum nitride is widely used as, for example, a substrate of semiconductor circuit components.
In particular, the sintered aluminum nitride having through-holes provided with internal conductive layers, known as via holes, is highly advantageously used because semiconductor external circuits can be electrically connected to each other through the via holes. With respect to the via holes formed in the sintered aluminum nitride, the arrangement, number, diameter, etc. thereof are determined variously in conformity with the design specification of desired substrate for semiconductor mounting.
As an advantageous method for furnishing the sintered aluminum nitride with via holes, there can be mentioned the co-firing method. The co-firing method comprises providing an aluminum nitride molding having through-holes for via hole formation, filling the through-holes for via hole formation with a conductive paste and firing the molding so as to simultaneously effect via hole firing and substrate sintering by one firing operation. This method enables producing the sintered aluminum nitride furnished with via holes efficiently through limited process steps, and is hence advantageous.
However, in the co-firing method, when the through-holes for via hole formation are highly isolated (that is, around one through-hole for via hole formation, other through-holes for via hole formation are not densely present), the influence of a shrinkage factor difference between conductive portions and sintered portions of aluminum nitride is so high around each of the highly isolated through-holes for via hole formation that a sintering balance is deteriorated. As a result, internal cracking of the sintered aluminum nitride and poor densification of via holes resulting in cracking of internal conductive portions and poor appearance have been experienced.
The resultant cracks tend to trap a gas, a liquid or impurities during the step of forming a thin film, for example, a thin film of conductive metal on a surface of the sintered product, and the expansion of trapped matter would cause film blisters. Further, dirt tends to stick to the sintered product surface, thereby inviting a decrease of film adhesion. Moreover, when a poor densification occurs at the above highly isolated via holes, the positional accuracy of via holes may be deteriorated.
Therefore, there has been a demand for the development of a process wherein the above problems would not occur even if an aluminum nitride molding having highly isolated through-holes for via hole formation is fired.
The inventors have made extensive and intensive studies with a view toward solving the above problems. As a result, it has been found that the above problems can be solved by furnishing an aluminum nitride molding with not only highly isolated through-holes for via hole formation but also through-holes for formation of dummy via holes not used for electrical connection. The present invention has been completed on the basis of this finding.
In particular, according to one aspect of the present invention, a process is provided for producing a sintered aluminum nitride furnished with via holes, comprising providing an aluminum nitride molding having through-holes for via hole formation and through-holes for formation of dummy via holes not used for electrical connection, filling the through-holes for via hole formation and the through-holes for dummy via hole formation with a conductive paste and firing the aluminum nitride molding and conductive paste.
In the above process, the aluminum nitride molding is furnished with the through-holes for via hole formation and the through-holes for dummy via hole formation so that the through-holes for via hole formation having been filled with the conductive paste and the aluminum nitride molding respectively exhibit a firing shrinkage factor (Xv, %) and a firing shrinkage factor (Xs, %) whose difference, (Xv-Xs,) is in the range of xe2x88x921.0 to 9.5%.
In another aspect of the present invention, there is provided a process for producing a sintered aluminum nitride furnished with via holes as mentioned above, wherein at least one of the through-holes for via hole formation is in such a highly isolated state that, therearound, other through-holes for via hole formation are not densely present, and wherein at least one of the through-holes for dummy via hole formation is formed around the through-hole for via hole formation of said highly isolated state.